What is PHP?

PHP is a server-side scripting language designed for web development, but which can also be used as a general-purpose programming language. PHP can be added to straight HTML or it can be used with a variety of templating engines and web frameworks. PHP code is usually processed by an interpreter, which is either implemented as a native module on the web-server or as a common gateway interface (CGI).

How to install more PHP extensions

Many extensions are already compiled into the image, so it’s worth checking the output of php -m or php -i before going through the effort of compiling more.

We provide the helper scripts docker-php-ext-configure, docker-php-ext-install, and docker-php-ext-enable to more easily install PHP extensions.

In order to keep the images smaller, PHP’s source is kept in a compressed tar file. To facilitate linking of PHP’s source with any extension, we also provide the helper script docker-php-source to easily extract the tar or delete the extracted source. Note: if you do use docker-php-source to extract the source, be sure to delete it in the same layer of the docker image.

Remember, you must install dependencies for your extensions manually. If an extension needs custom configure arguments, you can use the docker-php-ext-configure script like this example. There is no need to run docker-php-source manually in this case, since that is handled by the configure and install scripts.

See “Dockerizing Compiled Software” for a description of the technique Tianon uses for determining the necessary build-time dependencies for any bit of software (which applies directly to compiling PHP extensions).

PECL extensions

Some extensions are not provided with the PHP source, but are instead available through PECL. To install a PECL extension, use pecl install to download and compile it, then use docker-php-ext-enable to enable it:

It is strongly recommended that users use an explicit version number in their pecl install invocations to ensure proper PHP version compatibility (PECL does not check the PHP version compatiblity when choosing a version of the extension to install, but does when trying to install it).

For example, memcached-2.2.0 has no PHP version constraints (https://pecl.php.net/package/memcached/2.2.0), but memcached-3.0.4 requires PHP 7.0.0 or newer (https://pecl.php.net/package/memcached/3.0.4). When doing pecl install memcached (no specific version) on PHP 5.6, PECL will try to install the latest release and fail.

Beyond the compatibility issue, it’s also a good practice to ensure you know when your dependencies receive updates and can control those updates directly.

Unlike PHP core extensions, PECL extensions should be installed in series to fail properly if something went wrong. Otherwise errors are just skipped by PECL. For example, pecl install memcached-2.2.0 && pecl install redis-2.2.8 instead of pecl install memcached-2.2.0 redis-2.2.8. However, docker-php-ext-enable memcached redis is fine to be all in one command.

Other extensions

Some extensions are not provided via either Core or PECL; these can be installed too, although the process is less automated:

For running the FPM variants as an arbitrary user, the --user flag to docker run should be used (which can accept both a username/group in the container’s /etc/passwd file like --user daemon or a specific UID/GID like --user 1000:1000).

“E: Package 'php-XXX' has no installation candidate”

As of docker-library/php#542, this image blocks the installation of Debian’s PHP packages. There is some additional discussion of this change in docker-library/php#551 (comment), but the gist is that installing Debian’s PHP packages in this image leads to two conflicting installations of PHP in a single image, which is almost certainly not the intended outcome.

For those broken by this change and looking for a workaround to apply in the meantime while a proper fix is developed, adding the following simple line to your Dockerfile should remove the block (with the strong caveat that this will allow the installation of a second installation of PHP, which is definitely not what you’re looking for unless you really know what you’re doing):

RUN rm /etc/apt/preferences.d/no-debian-php

The proper solution to this error is to either use FROM debian:XXX and install Debian’s PHP packages directly, or to use docker-php-ext-install, pecl, and/or phpize to install the necessary additional extensions and utilities.

Configuration

It is strongly recommended to use the production config for images used in production environments!

The default config can be customized by copying configuration files into the $PHP_INI_DIR/conf.d/ directory.

Example

FROM php:7.2-fpm-alpine# Use the default production configurationRUN mv "$PHP_INI_DIR/php.ini-production""$PHP_INI_DIR/php.ini"# Override with custom opcache settingsCOPY config/opcache.ini $PHP_INI_DIR/conf.d/

Image Variants

The php images come in many flavors, each designed for a specific use case.

Some of these tags may have names like jessie or stretch in them. These are the suite code names for releases of Debian and indicate which release the image is based on.

php:<version>-cli

This variant contains the PHP CLI tool with default mods. If you need a web server, this is probably not the image you are looking for. It is designed to be used both as a throw away container (mount your source code and start the container to start your app), as well as a base from which to build other images.

It also is the only variant which contains the (not recommended) php-cgi binary, which is likely necessary for some things like PPM.

Note that all variants of php contain the PHP CLI (/usr/local/bin/php).

Apache without a Dockerfile

Changing DocumentRoot (or other Apache configuration)

Some applications may wish to change the default DocumentRoot in Apache (away from /var/www/html). The following demonstrates one way to do so using an environment variable (which can then be modified at container runtime as well):

This variant is highly recommended when final image size being as small as possible is desired. The main caveat to note is that it does use musl libc instead of glibc and friends, so certain software might run into issues depending on the depth of their libc requirements. However, most software doesn’t have an issue with this, so this variant is usually a very safe choice. See this Hacker News comment thread for more discussion of the issues that might arise and some pro/con comparisons of using Alpine-based images.

To minimize image size, it’s uncommon for additional related tools (such as git or bash) to be included in Alpine-based images. Using this image as a base, add the things you need in your own Dockerfile (see the alpine image description for examples of how to install packages if you are unfamiliar).

License

As with all Docker images, these likely also contain other software which may be under other licenses (such as Bash, etc from the base distribution, along with any direct or indirect dependencies of the primary software being contained).